Education leaders and much literature exhort teachers and school leaders to use data more often and more effectively to guide planning and decision making--called, "data driven decision making." This term is ubiquitous in literature and reform discourse, but "on the ground," so to speak, practitioners face significant challenges in analyzing, understanding, and applying data to improve practice. Obstacles faced by practitioners include insufficient expertise, tools, and time; also, organizational cultures in schools generally create few incentives for data analysis and as often as not sustain norms inimical to the collaboration and collective action required for data driven decision making. The case reported here illustrates these challenges through the actions of a principal identifying a problem of organizational culture and instructional practice and leading an initiative to promote collaboration, analysis, and reflection to help improve writing instruction in his school. (Contains 2 figures, 7 tables and 13 footnotes.)